I want to play Terraria with the same players and worlds on two different computers. It looks like the files must be in My Documents\My Games\Terraria.

Is there a way to sync those files between two or more computers (using Dropbox or AeroFS for example) so that when I play on one computer, the player and world files will automatically update on the other computer?

Repeat steps 4 and 5 on each additional computer that you want your characters and worlds to be available on.

Another option, perhaps even simpler, is to use BitTorrent Sync to synchronize the Terraria folders on two computers. If you use BitTorrent Sync you do not have to move the folders and make links. You can sync them in-place.